Off-white and gray autodeposition coatings

ABSTRACT

A composition for coating a metal substrate with a white to off-white or gray colored autodeposited coating comprising water, polymeric resin, HF and pigment particles comprising a core of titanium dioxide, an intermediate zirconia and/or alumina layer, and an outer organic layer, optionally the particles are treated with an anionic surfactant.

CROSS REFERENCE TO RELATED APPLICATIONS

This invention claims priority from the U.S. Provisional Application,Ser. No. 60/845,322, filed Sep. 18, 2006.

FIELD OF THE INVENTION

This invention relates to compositions and processes for generatingpigmented polymeric coatings on metal substrates by chemical reactionbetween the metal and an autodeposition coating bath using pigmentparticles, which have been stabilized against the autodeposition bath,instead of or in addition to conventional carbon black particles. Moreparticularly, the invention relates to white to off-white and graycoatings generated by an autodeposition coating bath, as well asprocesses of depositing the coatings, the autodeposition coating bathsthemselves, concentrates for forming the baths.

BACKGROUND OF THE INVENTION

Autodeposition has been in commercial use on steel for about thirtyyears and is now well established for that use. For details, see forexample, U.S. Pat. No. 3,592,699 (Steinbrecher et al.); U.S. Pat. Nos.4,108,817 and 4,178,400 (both to Lochel); U.S. Pat. No. 4,180,603(Howell. Jr.); U.S. Pat. Nos. 4,242,379 and 4,243,704 (both to Hall etal.); U.S. Pat. No. 4,289,826 (Howell, Jr.); and U.S. Pat. No. 5,342,694(Ahmed) as well as U.S. Pat. No. 5,500,460 (Ahmed et al.) and U.S. Pat.No. 6,645,633 (Weller et al.). The disclosures of all of these patentsare hereby incorporated by reference.

Autodeposition compositions are usually in the form of liquid, usuallyaqueous, solutions, emulsions or dispersions in which active metalsurfaces of inserted objects are coated with an adherent resin orpolymer film that increases in thickness the longer the metal objectremains in the bath, even though the liquid is stable for a long timeagainst spontaneous precipitation or flocculation of any resin orpolymer, in the absence of contact with active metal. “Active metal” isdefined as metal that is more active than hydrogen in the electromotiveseries, i.e., that spontaneously begins to dissolve at a substantialrate (with accompanying evolution of hydrogen gas) when introduced intothe liquid solution, emulsion or dispersion. Such compositions, andprocesses of forming a coating on a metal surface using suchcompositions, are commonly denoted in the art, and in thisspecification, as “autodeposition” or “autodepositing” compositions,dispersions, emulsions, suspensions, baths, solutions, processes,methods, or a like term. Autodeposition is often contrasted withelectrodeposition, which can produce very similar adherent films butrequires that metal or other objects to be coated be connected to asource of direct current electricity for coating to occur. No suchexternal electric current is used in autodeposition, instead anaccelerator is used.

The autodeposition accelerator component is a substance such as an acid,oxidizing agent, and/or complexing agent capable of causing thedissolution of active metals from active metal surfaces in contact withthe autodeposition composition thereby driving the coating deposition.The autodeposition accelerator component can be chosen from the groupconsisting of hydrofluoric acid and its salts, fluosilicic acid and itssalts, fluotitanic acid and its salts, ferric ions, acetic acid,phosphoric acid, sulfuric acid, nitric acid, hydrogen peroxide, peroxyacids, citric acid and its salts, and tartaric acid and its salts. Theautodeposition accelerator component may be selected from any materialor combination of materials known for this purpose in priorautodeposition art or otherwise found to give satisfactory results.

Autodeposition compositions typically may also contain one or moreadditional ingredients. Such additional ingredients may includesurfactants (emulsifying or dispersing agents), fillers, biocides, foamcontrol agents, flow control (leveling) agents, and/or carbon blackpigments.

Autodeposition coatings, in the absence of pigment, tend to be colorlessor slightly yellow to green, and do not provide adequate hiding powerfor many commercial uses. Adding pigment is a conventional way toincrease hiding power of coatings. Introducing pigment intoautodeposition baths has proven to be problematic due to the stronglyacidic nature of the baths, which have a pH ranging from 1.0 to 4.0.Previously, autodeposition coatings have been limited to black color,using so called “carbon black” pigments that were stable in acid anddispersible in the working bath.

Conventional pigments are adapted for use in paints, which typicallyhave a pH ranging from 5.5 to 10. The significant difference in pHbetween paint and autodeposition baths has limited the pigments that canbe used in autodeposition baths due to the lack of pigments that arepredictably stable in acidic autodeposition baths. Attempts to introducea non-carbon black pigment into autodeposition to produce a coating incolors other than black have up to now been unsuccessful due tounpredictable behaviors of various pigments, including dissolving intothe bath, failing to deposit on the active metal substrate with thepolymer, developing coatings that rinsed off of the active metalsubstrate, and reaction in the bath with other components resulting in“crashing” of the bath, as well as settling out of dispersion to formsludge on the tank bottom.

A particular problem in formulating a white or off-white autodepositioncoating has been the limited stability of pigments in the autodepositionbath, which typically is subject to the periodic addition of oxidizingagents and contains strong acid. In particular, titanium dioxide (TiO₂),an economical and commonly used white pigment, is unstable inautodeposition bath chemistry due to the presence of hydrogen fluoride(HF). In the presence of HF, TiO₂ hydrolyzes to fluorotitanic acid andthe bath becomes unstable. These changes to the titanium dioxide make itunavailable for deposition on metal substrates as a white pigment forgenerating white, off-white or gray coatings. Another drawback of priorattempts to use titanium dioxide particles alone has been that theparticles do not remain dispersed and form sludge which requiresdisposal.

SUMMARY OF THE INVENTION

This invention relates to the use of aqueous liquid compositions(solutions or dispersions) with which active metal surfaces can becoated, by mere contact with the liquid composition, with an adherentwhite to off-white or gray polymer film that increases in thickness thelonger the time of contact, even though the liquid composition is stablefor a long time against spontaneous precipitation or flocculation of anysolid polymer, in the absence of contact with active metal. (For thepurposes of this application, the term “active metal” is to beunderstood as including iron and all the metals and alloys more activethan iron in the electromotive series.) Such liquid compositions aredenoted in this specification, and commonly in the art, as“autodeposition” or “autodepositing” compositions, dispersions,emulsions, suspensions, baths, solutions, or a like term.

It is an object of the invention to provide an autodeposition bathcomposition for use in coating an active metal surface comprising: anaqueous solution of an autodeposition accelerator comprising acid, in anamount such that the composition has a pH of about 1.6 to about 3.8, andat least one oxidizing agent; particles of a coating-forming polymericmaterial dispersed throughout the composition; a component of non-blacksolid pigment particles, stabilized against the acid, dispersedthroughout the composition; an emulsifying component comprising anionicsurfactant; optionally, a second stabilizing surfactant different fromthe emulsifying component; and, optionally, finely divided solidssuitable as fillers and/or black pigment in the coatings to be formedfrom the composition; the composition being effective to chemicallyattack, in the absence of an external electrical potential, an activemetal surface immersed therein to dissolve therefrom metal to releaseions of the metal and sufficient to cause the polymeric material and thenon-black solid pigment particles to deposit on the active metal surfacein the form of an initially adherent coating which increases in weightor thickness the longer the time the surface is immersed in thecomposition.

It is a further object of the invention to provide a composition whereinthe acid is hydrofluoric and the non-black solid pigment particlescomprise a titanium dioxide core, a first coating of an inorganicmaterial, desirably an oxide different from titanium dioxide and asecond coating of an organic material. The first coating of an oxide maycomprise oxides that are substantially insoluble in the acid. In oneembodiment of the invention the oxides are selected from alumina,zirconia and mixtures thereof. It is a yet further object of theinvention to provide a composition wherein the second coating of anorganic material comprises an anionic dispersing additive, a cationicdispersing additives or a non-ionic dispersing additive.

In one embodiment of the invention, the second coating of an organicmaterial comprises at least one of polyacrylates, polyphosphates,cationized polyacrylates, epichlorhydrine resins, dicyandiamide resins,polymethacrylates, polyether polyols and polyesters. In anotherembodiment, the polymethacrylates are selected from quaternarydimethylaminoethyl methacrylates, melamine-formaldehyde resins andmixtures thereof.

It is a further object of the invention to provide a composition whereinthe weight ratio of the non-black solid pigment particles to thepolymeric material ranges, in increasing order of preference, from about1, 2.5, 5, 7.5, 10, 15, 20, 25, 26, 27, or 28 and is less than, inincreasing order of preference, 50, 49, 48, 47, 46, 45, 44, 43, 42, 41,40, 39, 38, 37, 36, 35, 34, 33, 32, or 31.

It is a further object of the invention to provide a composition whereinthe anionic surfactant is selected from surfactants having at least onesulfate, sulphonate, phosphate, or phosphonate functional group.

It is a further object of the invention to provide a composition whereinthe anionic surfactant maintains dispersion of the particles of acoating-forming polymeric material, and the component of non-black solidpigment particles, such that the polymeric material and the pigmentparticles deposit on the active metal surface in the form of aninitially adherent coating.

It is another object of the invention to provide a composition whereinthe composition comprises an amount of black pigment sufficient toprovide a gray coating formed from the composition.

It is a further object of the invention to provide a composition whereinthe polymeric material is selected from the group consisting ofstyrene-butadiene, acrylonitrile-butadiene, polyethylene, acrylic,tetrafluoroethylene, polyvinyl chloride, urethane resins,styrene-acrylic, epoxy, and epoxy-acrylic materials.

It is a further object of the invention to provide a composition whereinthe oxidizing agent is selected from the group consisting of hydrogenperoxide, dichromate, perborate, bromate, permanganate, nitrite, nitrateand chlorate.

It is a further object of the invention to provide a composition whereinthe acid is selected from the group consisting of hydrofluoric,sulfuric, hydrochloric, nitric, phosphoric, hydrobromic, hydroiodic,acetic, chloroacetic, trichloroacetic, lactic, tartaric and polyacrylic.

It is another object of the invention to provide a method of depositinga white to off-white or gray autodeposition coating on an active metalsubstrate surface comprising:

-   -   contacting an active metal substrate surface for 0.5 to 10        minutes, with a composition according to any one of claims 1 to        15 to form a white to off-white or gray initially adherent        coating on the surface;    -   rinsing the initially adherent coating with a rinse comprising        water;    -   optionally, drying the initially adherent coating; and    -   curing the initially adherent coating to form a cured, white to        off-white or gray coating.

It is another object of the invention to provide an aqueousautodeposition concentrate composition for use in forming anautodeposition bath comprising:

-   -   particles of a coating-forming polymeric material dispersed        throughout the composition;    -   non-black solid pigment particles comprising a titanium dioxide        core, a first coating of an oxide different from titanium        dioxide and a second coating of an organic material, the        particles dispersed throughout the composition;    -   an emulsifying component comprising anionic surfactant;    -   optionally a second stabilizing surfactant different from the        emulsifying component; and    -   optionally finely divided solids suitable as fillers and/or        carbon black pigment in the coatings to be formed from the        composition;    -   wherein the weight ratio of the non-black solid pigment        particles to the polymeric material ranges from 1-49% by weight.

Except in the operating examples, or where otherwise explicitlyindicated, all numerical quantities in this description indicatingamounts of material or reaction conditions are to be understood asmodified by the word “about”.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 depicts a cross-sectional view of one type of titanium dioxidepigment useful in the invention.

DETAILED DESCRIPTION OF EMBODIMENTS

Applicants have developed a white to off-white or gray coloredautodeposition coating suitable for use as a stand alone coating or as aprimer for general industrial application that comprises titaniumdioxide pigment particles either alone or in combination with blackpigment, such as carbon black. The instability of autodepositionconcentrates and baths using ordinary titanium dioxide pigment particleshas been overcome by developing a new autodepositing bath compositionhaving titanium dioxide particles that have been stabilized against thebath.

The first difficulty encountered in making a stable titanium dioxideautodeposition coating bath was the instability of the titanium dioxideparticle in the acidic environment of the autodeposition bath. In theabsence of any additional outer coating layer, such as an organic layer,deposited on titanium dioxide particles, the acidity of theautodeposition bath will dissolve or hydrolyze the titanium dioxide. Inparticular hydrofluoric acid will react with titanium dioxide togenerate fluorotitanic acid.

Autodeposition baths contain an accelerator component that desirablycomprises ferric cations, hydrofluoric acid, and hydrogen peroxide. In aworking composition according to the invention, independently for eachconstituent: the concentration of ferric cations preferably is at least,with increasing preference in the order given, 0.5, 0.8, or 1.0 g/l andindependently preferably is not more than, with increasing preference inthe order given, 2.95, 2.90, 2.85, 2.80, or 2.75 g/l; the concentrationof fluorine in anions preferably is at least, with increasing preferencein the order given, 0.5, 0.8, 1.0, 1.2, 1.4, 1.50, 1.55, 1.60, 1.80, 2.0g/l and independently preferably is not more than, with increasingpreference in the order given, 20, 17, 15, 13, 12, 11, 10, 7.0, 5.0, or4.0 g/l; and the amount of hydrogen peroxide added to freshly preparedworking composition preferably is at least, with increasing preferencein the order given, 0.050, 0.10, 0.20, 0.30, or 0.40 g/l andindependently preferably is not more than, with increasing preference inthe order given, 2.1, 1.8, 1.5, 1.2, 1.00, 0.90, or 0.80 g/l.

Preferably, an accelerator component is selected which is sufficient instrength and amount to impart to the autodeposition composition anoxidation-reduction potential, measured by the potential of a platinumor other inert metal electrode in contact with the autodepositing liquidcomposition, that is, with increasing preference in the order given, atleast 150, 175, 200, 225, or 250 mV more oxidizing than a standardhydrogen electrode and independently preferably is, with increasingpreference in the order given, not more than 550, 525, 500, 475, or 450mV more oxidizing than a standard hydrogen electrode. Desirably theaccelerator component also comprises a source of hydrogen cations, i.e.acid, in an amount sufficient to impart to the autodeposition bath a pHthat is at least, with increasing preference in the order given, 1.0,1.4, 1.6, 1.8, or 2.0 and independently preferably is not more than,with increasing preference in the order given, 3.8, 3.6, 3.2, 3.0, 2.8,or 2.6.

Typically titanium dioxide particles are stabilized with alumina andsilica. Silica is unstable in HF, as to some extent is alumina in HF.Thus far, silica coated particles have not proven to be stable againstHF; desirably, the coatings on the titanium dioxide particles comprise,in increasing order of preference, less than 30, 20, 10, 5, 4, 3, 2, 1wt % silica. In testing titanium dioxide particles coated with alumina,aluminum leached from the titanium dioxide particles into theautodeposition bath to form aluminum fluoride. The aluminum leachingphenomenon was found to be correctable by increasing the amount of HF inthe bath. In additional testing, zirconia either alone or combined withalumina was found to protect the titanium dioxide from the acidicenvironment of the autodeposition bath.

A second hurdle to producing a stable, white to off-white or grayautodeposition bath was maintaining titanium dioxide suspended in theaqueous autodeposition concentrates and baths, and ensuring the desiredamount of deposition of both the polymer and the pigment particles.Desirably, in one embodiment there is relatively equal depositionbetween polymeric particles and pigment particles.

It was found that hydrophobicity/hydrophilicity of the titanium dioxideparticles and hydrophobicity/hydrophilicity of the polymeric particles,relative to each other are variables in controlling whether titaniumdioxide particles remain dispersed in the bath and deposit adherently onthe active metal substrate to achieve the desired color.

The type of surfactant used and composition of the surfactant used forthe polymeric particles affects the relative compatibility, thus therelative deposition rate, between polymeric and pigment particles.Without being bound by a single theory, it is hypothesized thathydrophobic polymeric particles used in conjunction with hydrophilictitanium dioxide particles caused surfactant in the autodeposition bathto migrate toward the emulsion particles leaving the titanium dioxidepigment deprived of surfactant and eventually causing the titaniumdioxide particle to settle out of dispersion. Selection of a morehydrophilic surfactant results in more surfactant being available to aidin dispersing the pigment particles. Desirably, there is relativelyequal partitioning of surfactant between the two particles and anequilibrium condition is maintained such that the dispersion of polymerparticles and pigment particles is stable in the absence of activemetal.

In some embodiments, the emulsifying component of anionic surfactant issufficient to provide adequate stability to the anionically stabilizedpolymer particles and to the non-white solid pigment particles.Generally, the polymer particles in an autodeposition bath areanionically stabilized. This polymer stabilization may be achieved, asis known in the art, by either incorporating an anionic surfactant intothe polymer or by adding anionic surfactant to the polymer emulsion. Insome cases, both means are used. This emulsifying component comprisinganionic surfactant may be sufficient to achieve stable dispersion andadequate deposition of the solid pigment particles in addition to thepolymer particles.

In other embodiments, a second stabilizing surfactant may be included tofurther contribute to stable dispersion and adequate deposition of thesolid pigment particles.

The surfactant package, meaning the emulsifying component and any secondstabilizing surfactant different from the emulsifying component, shouldbe selected and should be present in sufficient concentration toemulsify or disperse the polymer particles and disperse the pigmentparticles in the autodeposition composition so that no separation orsegregation of bulk phases that is perceptible with normal unaided humanvision occurs during storage at 25° C. for at least 24 hours afterpreparation of the autodeposition composition, in the absence of contactof the autodeposition composition with any active metal.

Anionic surfactants are generally preferred, although amphoteric as wellas nonionic surfactants may also be utilized. Anionic surfactants usefulin the present invention include anionic surfactant having sulfate,sulphonate, phosphate, or phosphonate end groups. In one embodiment, theanionic surfactant used for coating the titanium dioxide pigmentparticles and stabilizing the polymer particles is selected fromalkoxylated ether sulfates, such as by way of non-limiting example,Polystep B-40; Rhodapex™ CO-128, -433, and -436 and Texapon™ E-12 andK-12.

Modified TiO₂ particles have been successfully tested in autodepositionbaths for decomposition and ability to deposit on the metal substrate.Desirably, the modified titanium dioxide particles are sufficientlystable in acidic conditions generally found in the autodeposition bath;and, in a particular embodiment, are sufficiently stable in the presenceof HF, such that the solid pigment particles remain available fordeposition on the metal substrates placed in the autodeposition bath. Itis believed that the particles do not hydrolyze, however levels ofhydrolysis of the pigment particles which do not interfere withdeposition and bath stability are acceptable.

Performance properties (chemical, photochemical and physicalcharacteristics) are determined principally by at least the followingfeatures of pigment particles: the particle size of the pigment and thechemical composition of the surface of the pigment particles. Thechemical composition of the surface of the TiO₂ particles is modified bycoating them with an inorganic layer of a second material different fromtitanium dioxide.

Many commercial grades of TiO₂ have inorganic and in some cases organicsurface treatments, not all of which are suitable for use inautodeposition baths. Inorganic surface modifiers most often used fortitanium dioxide are precipitated coatings of alumina and silica.Applicants research has shown that, for use in autodeposition baths, itis desirable that the first layer comprise an inorganic material havinglow solubility in the acid used in the autodeposition bath, generallythis is HF. Preferably, the inorganic material is substantiallyinsoluble in the acid used in the autodeposition bath. As used herein,“substantially insoluble” means that the material has a solubility atambient temperature of less than, in order of increasing preference,0.5, 0.25, 0.1, 0.075, 0.05, 0.025, 0.01, 0.0075, 0.005, 0.0025, or0.001 g/100 ml of the acid. Preferably, the inorganic layer is a metaloxide, such as by way of non-limiting example zirconia and/or alumina.

Once coated with a first layer, i.e. the inorganic layer, the pigmentparticles are coated with second layer that is an organic layer.Alternatively, the pigment particles may be simultaneously contactedwith the inorganic and organic materials thereby forming a firstinorganic layer and a second outer organic layer; or a composite coatingmay be formed.

Generally, components of the organic layer are selected from substances,known to those of skill in the pigment art, which are useful indispersing solid pigment in an aqueous liquid medium, such as by way ofnon-limiting example, anionic additives, cationic additives andnon-ionic additives that assist in dispersing the particles withoutinterfering with deposition of the particles on metallic substratesduring the autodeposition process.

Suitable anionic additives include for example polyacrylates orpolyphosphates and the like; cationic additives include for examplecationized polyacrylates or polymethacrylates, such as quaternarydimethylaminoethyl methacrylates or melamine-formaldehyde resins,epichlorhydrine resins, dicyandiamide resins and the like. Non-ionicadditives include polyols and/or polyesters and the like. A number ofother suitable coatings for pigments are recited in U.S. Pat. No.3,825,438, incorporated herein by reference.

FIG. 1 is a cross-sectional view of a pigment particle useful in theinvention. In this embodiment, pigment particles comprise a core of TiO₂(1) coated with a mixed zirconia/alumina layer (2) followed by an outerorganic layer (3), see FIG. 1. Optionally, the coated TiO₂ pigment maybe subsequently treated with anionic surfactant that forms a third outerlayer (4). Desirably the anionic surfactant is based on sulfatechemistry, that is has sulfate functional groups, to promote uniformdeposition and consumption rate of the pigment particles to that of thepolymer emulsion particles.

The inner first inorganic layer and second organic layer surfacetreatment of the TiO₂ core in conjunction with the post treatment withanionic surfactant provides a stable and depositable TiO₂ pigment slurryin the acidic HF containing autodeposition baths. With the successfulincorporation of the modified TiO₂ particles into the autodepositionbath, the autodeposition coating process provides coatings in thetraditional black, white to off-white, and in shades of gray. The colorof the coating is a function of the amount of conventional black pigmentused in conjunction with the titanium dioxide pigment.

Autodeposition coatings comprising modified TiO₂ particles depositedfrom autodeposition baths containing these particles have been testedand displayed corrosion resistance and physical performance similar tothe black commercial counterpart. Panels coated in baths havingdifferent amounts of modified TiO₂ particles coat metal substrates witha polymeric coating in uniform shades of white to gray. The resultingcoated panels showed consistency in the compositions' performance incolor, hiding power, and tinting strength.

One embodiment of the invention provides a composition for depositing anaqueous off-white autodeposition coating comprising: modified TiO₂particles and at least one emulsion polymer. Desirably the modified TiO₂particles are provided as an aqueous slurry to aid in incorporation ofthe component into the composition. Optionally, the TiO₂ slurry isfurther modified with anionic surfactant, desirably based on sulfate,sulphonate, phosphate, or phosphonate end groups. Alternatively, anionicsurfactant and the slurry containing the modified TiO₂ particles can beadded separately to the bath. The emulsion polymer(s) can be acrylic,styrene-acrylic, epoxy, epoxy-acrylic, polyurethane dispersion, or anyother water dispersible ionically stabilized polymers suitable for usein autodeposition processes, as are known to those skilled in the art.

Another embodiment of the invention provides an aqueous compositionsuitable for depositing gray autodeposition coatings on metal substratescomprising: modified TiO₂ pigment particles, black pigment particles,preferably carbon black, and at least one emulsion polymer. Desirably,both pigments are provided as aqueous slurries to aid in incorporationinto the composition and the carbon black slurry is anionicallystabilized. Optionally, the TiO₂ slurry is further modified with anionicsurfactant, desirably based on sulfate, sulphonate, phosphate, orphosphonate end groups. Alternatively, anionic surfactant and the slurrycontaining the modified TiO₂ particles can be added separately to thebath. The emulsion polymer(s) can be acrylic, styrene-acrylic, epoxy,epoxy-acrylic, polyurethane dispersion, or any other water dispersibleionically stabilized polymers suitable for use in autodepositionprocesses, as are known to those skilled in the art.

In another aspect of the invention, autodeposition coating baths areprepared by mixing one of the above-described autodepositioncompositions with water, HF, iron and hydrogen peroxide in amountssufficient to form an autodeposition bath wherein the percent ofnon-volatiles is in the range of 1-20 weight %.

The practice of this invention may be further appreciated from thefollowing working examples.

Example 1

A 35% non-volatile, off-white autodeposition coating compositionconcentrate was formulated as follows:

To a 1.5 liter container, were added 211.65 g of deionized water, 5.63 gof anionic surfactant having 20% non-volatile (active), 786.4 g ofanionically modified polymer emulsion having 42+/−1% non-volatile, and132.6 g of TiO₂ pigment slurry having 50+/−1% non-volatile. The activepigment to polymeric binder ratio was 20%. The TiO₂ pigment in theslurry was described by the manufacturer as having a first inner layerof zirconia and alumina and a second outer layer of polyether polyol.The TiO₂ pigment and the polymer particles remain uniformly dispersed inthe concentrate.

Example 2

A 6% non-volatile, 20 ml Fe titration, off-white autodeposition coatingbath was formulated using the composition of Example 1, as follows:

In a 1.5 liter container, the following were combined:

5.20 g HF 1.70 g Iron powder 3.62 g Hydrogen peroxide 35% Distilledwater to make 1.0 literThe material was mixed for several minutes. 257.1 g of the compositionof EXAMPLE 1 was added to the 1.5 liter container slowly with agitation.Finally, sufficient distilled water to make 1.5 liters was added. Thebath was mixed for one hour and bath parameters were adjusted to thefollowing parameters under continuous agitation:

Redox Value 275-400 mV Lineguard 101 meter reading 100-700 microamperesTotal % non-volatile 1-10% Wet coating solids 20-50% Starter titration10-40 ml Bath temperature 20-25° F. Conductivity 1,200-10,000microsiemensAfter the off-white bath was prepared and parameters optimized, metallicpanels were treated according to the following method:

-   A. Cleaning with alkaline cleaner—2 minutes-   B. Warm water rinsing—1 minute-   C. Deionized water rinsing—1 minute-   D. Contacting with the off-white autodeposition processing bath of    Example 2-2 minutes-   F. Water rinsing—1 minute-   G. Treating with AUTOPHORETIC® Reaction Rinse E2 (commercially    available from Henkel Corporation)—1 minute-   H. Oven curing at 53° C. for 7 minutes and at 185° C. for 40    minutes.    The resulting coated panels were slightly off-white in color, were    uniform in color and exhibited good hiding power.

Example 3

A 35% non-volatile, grey autodeposition coating composition concentratewas formulated as follows:

To a one-liter flask, were added 211.14 g of deionized water, 5.63 g ofanionic surfactant having 20% non-volatile (active), 3.38 g of blackpigment slurry having 30% non-volatile, 786.4 g of anionically modifiedpolymer emulsion having 42+/−1% non-volatile, and 132.6 g of the TiO₂pigment slurry of Example 1 having 50+/−1% non-volatile. The activepigment to polymeric binder ratio was 20%.

A 6% non-volatile, 20 ml Fe titration, gray autodeposition coating bathwas formulated using the composition of Example 3, according to theprocedure of Example 2.

The bath was mixed for one hour and bath parameters were adjusted to theparameters of Example 2 under continuous agitation.

After the gray bath was prepared and parameters optimized, metallicpanels were treated according to the method of Example 2. The resultingcoated panels were gray in color, were uniform in color and exhibitedgood hiding power.

Example 4

Gray autodeposition baths were formulated according to Example 3, atvarious pigment to binder ratios. The ratios varied from 5:95pigment:binder to 50:50 pigment:binder. The physical and corrosionperformance at various ratios are shown in Table 1, below:

TABLE 1 Neutral Salt Spray Cross (Total mm hatch Solvent Pencil scribeadhesion Resistance Hardness creep at ASTM Reverse M.E.K. ASTM 504hours) Pigment:Binder D 3359- Impact Double D3363- ASTM ratio 02 (in.lb.) Rubs 00 B117 Stability  5:95 5B >80 >200 >3H 1.6 Stable 10:905B >80 >200 >3H 1.5 Stable 17:87 5B >80 >200 >3H 2.9 Stable 30:705B >80 >200 >3H 1.2 Stable 40:60 5B >80 >200 >3H 1.4 Stable 50:505B >80 >200 >3H Not tested *Not stable *Not stable means that the TiO₂was not deposited and settled out of the autodeposition bath.

Example 5 Comparative Example

A 35% non-volatile, gray autodeposition coating composition concentratewas formulated as follows:

To 1.5 liter flask, were added 92.7 g of deionized water, 5.63 g ofanionic surfactant having 20% non-volatile (active), 3.38 g of blackpigment slurry having 30% non-volatile, 904.89 g of anionically modifiedpolymer emulsion having 42+/−1% non-volatile, and 132.6 g of TiO₂pigment slurry of Example 1 having 50+/−1% non-volatile. The activepigment to polymeric binder ratio was 20%.

The surfactant used to make the emulsion in this example was changedrelative to the previous examples. The surfactant used had similar ionicend groups to the surfactant of Examples 1-4, but the number moles ofalkoxylation was reduced making the surfactant of Example 5 lesshydrophilic.

A 6% non-volatile, 20 ml Fe titration, gray autodeposition coating bathwas formulated using the composition of Example 5, according to theprocedure of Example 2.

The bath was mixed for one hour and bath parameters were adjusted to theparameters of Example 2 under continuous agitation. After the gray bathwas prepared and parameters optimized, metallic panels were treatedaccording to the method of Example 2. The resulting coated panels werebrown in color indicating no pigment deposition. After aging of theautodeposition bath for a few days, the pigment was separated from thebath or destabilized. Changing bath hydrophobic/hydrophilic equilibriumbetween emulsion and pigment particles caused un-equal partitioning ofthe surfactant between the particles, depriving the pigment particlesfrom surfactant, and therefore destabilization of the pigment particlesoccurred.

1. An autodeposition bath composition for use in coating an active metalsurface comprising: a. an aqueous solution of an autodepositionaccelerator comprising an acid, in an amount such that the compositionhas a pH of about 1.6 to about 3.8, and at least one oxidizing agent; b.particles of a coating-forming polymeric material uniformly dispersedthroughout the composition; c. a component of non-black solid pigmentparticles, stabilized against said acid, uniformly dispersed throughoutthe composition; d. an emulsifying component comprising an anionicsurfactant; and, optionally, e. black pigment and/or finely dividedsolids suitable as fillers in the coatings to be formed from thecomposition; said composition being effective to chemically attack, inthe absence of an external electrical potential, an active metal surfaceimmersed therein to dissolve therefrom metal to release ions of saidmetal and sufficient to cause said polymeric material and said non-blacksolid pigment particles to deposit on the active metal surface as aninitially adherent coating which increases in weight or thickness thelonger the time said surface is immersed in said composition; whereinrelative hydrophobicity/hydrophilicity of the non-black solid pigmentparticles and hydrophobicity/hydrophilicity of the particles of acoating-forming polymeric material are selected such that the non-blacksolid pigment particles remain dispersed in the bath and depositadherently on the active metal substrate.
 2. The composition accordingto claim 1 wherein said acid is hydrofluoric and said non-black solidpigment particles comprise a titanium dioxide core, a first coating ofan oxide different from titanium dioxide and a second coating of anorganic material.
 3. The composition according to claim 2 wherein saidfirst coating of an oxide comprises oxides that are substantiallyinsoluble in said acid.
 4. The composition according to claim 2 whereinsaid first coating of an oxide comprises oxides selected from alumina,zirconia and mixtures thereof.
 5. The composition according to claim 2wherein said second coating of an organic material comprises an anionicdispersing additive, a cationic dispersing additives or a non-ionicdispersing additive.
 6. The composition according to claim 2 whereinsaid second coating of an organic material comprises at least one ofpolyphosphates, epichlorohydrin resins, dicyandiamide resins, polyolsand polyesters.
 7. The composition according to claim 1 having a weightratio of the non-black solid pigment particles to the polymeric materialthat ranges from 1-49% by weight.
 8. The composition according to claim1 wherein said anionic surfactant is selected from surfactants having atleast one sulfate, sulphonate, phosphate, or phosphonate functionalgroup.
 9. The composition according to claim 1 wherein said anionicsurfactant maintains dispersion of the particles of a coating-formingpolymeric material, and the component of non-black solid pigmentparticles, such that said polymeric material and said pigment particlesdeposit on the active metal surface as an initially adherent coating.10. The composition according to claim 1 wherein said compositioncomprises an amount of black pigment sufficient to provide a graycoating formed from the composition.
 11. The composition according toclaim 1 wherein said polymeric material is selected from the groupconsisting of styrene-butadiene, acrylonitrile-butadiene, polyethylene,acrylic, tetrafluoroethylene, polyvinyl chloride, urethane resins,styrene-acrylic, epoxy, and epoxy-acrylic materials.
 12. The compositionaccording to claim 1 wherein said oxidizing agent is selected from thegroup consisting of hydrogen peroxide, dichromate, perborate, bromate,permanganate, nitrite, nitrate and chlorate.
 13. The compositionaccording to claim 1 wherein said acid is selected from the groupconsisting of hydrofluoric, sulfuric, hydrochloric, nitric, phosphoric,hydrobromic, hydroiodic, acetic, chloroacetic, trichloroacetic, lactic,tartaric and polyacrylic.
 14. The composition according to claim 1wherein said oxidizing agent is hydrogen peroxide.
 15. The compositionaccording to claim 1 wherein said acid comprises hydrofluoric acid andthe coating-forming polymeric material is selected from epoxy orepoxy-acrylic material.
 16. The composition according to claim 15wherein said non-black solid pigment particles comprise a titaniumdioxide core, a first coating of an oxide comprising zirconia and asecond coating of an organic material.
 17. An autodeposition bathcomposition for use in coating an active metal surface comprising: a. anaqueous solution of an autodeposition accelerator comprising an acid, inan amount such that the composition has a pH of about 1.6 to about 3.8,and at least one oxidizing agent; b. particles of a coating-formingpolymeric material uniformly dispersed throughout the composition; c. acomponent of non-black solid pigment particles, stabilized against saidacid, uniformly dispersed throughout the composition; d. a surfactantpackage comprising an emulsifying component comprising an anionicsurfactant and optionally a second stabilizing surfactant different fromthe emulsifying component; and, optionally, e. black pigment and/orfinely divided solids suitable as fillers in the coatings to be formedfrom the composition; wherein b.), c.) and d.) are selected such thatpartitioning of d.) between b.) and c.) provides an equilibriumcondition such that dispersion of polymer particles and pigmentparticles is maintained in the absence of active metal; and saidcomposition remains effective to chemically attack an active metalsurface immersed therein to dissolve therefrom metal to release ions ofsaid metal and sufficient to cause said polymeric material and saidnon-black solid pigment particles to deposit on the active metal surfaceas an initially adherent coating which increases in weight or thicknessthe longer the time said surface is immersed in said composition;wherein relative hydrophobicity/hydrophilicity of the non-black solidpigment particles and hydrophobicity/hydrophilicity of the particles ofa coating-forming polymeric material are selected such that thenon-black solid pigment particles remain dispersed in the bath anddeposit adherently on the active metal substrate.
 18. The compositionaccording to claim 17 wherein said acid is hydrofluoric and saidnon-black solid pigment particles comprise a titanium dioxide core, afirst coating of an oxide different from titanium dioxide and a secondcoating of an organic material.
 19. The composition according to claim18 wherein said first coating of an oxide comprises oxides that aresubstantially insoluble in said acid.
 20. The composition according toclaim 18 wherein said first coating of an oxide comprises oxidesselected from alumina, zirconia and mixtures thereof.
 21. Thecomposition according to claim 18 wherein said second coating of anorganic material comprises an anionic dispersing additive, a cationicdispersing additives or a non-ionic dispersing additive.
 22. Thecomposition according to claim 18 wherein said second coating of anorganic material comprises at least one of polyphosphates,epichlorohydrin resins, dicyandiamide resins, polyols and polyesters.23. The composition according to claim 17 having a weight ratio of thenon-black solid pigment particles to the polymeric material that rangesfrom 1-49% by weight.
 24. The composition according to claim 17 whereinsaid anionic surfactant is selected from surfactants having at least onesulfate, sulphonate, phosphate, or phosphonate functional group.
 25. Thecomposition according to claim 17 wherein said anionic surfactantmaintains dispersion of the particles of a coating-forming polymericmaterial, and the component of non-black solid pigment particles, suchthat said polymeric material and said pigment particles deposit on theactive metal surface as an initially adherent coating.
 26. Thecomposition according to claim 17 wherein said composition comprises anamount of black pigment sufficient to provide a gray coating formed fromthe composition.
 27. The composition according to claim 17 wherein saidpolymeric material is selected from the group consisting ofstyrene-butadiene, acrylonitrile-butadiene, polyethylene, acrylic,tetrafluoroethylene, polyvinyl chloride, urethane resins,styrene-acrylic, epoxy, and epoxy-acrylic materials.
 28. The compositionaccording to claim 17 wherein said oxidizing agent is selected from thegroup consisting of hydrogen peroxide, dichromate, perborate, bromate,permanganate, nitrite, nitrate and chlorate.
 29. The compositionaccording to claim 17 wherein said acid is selected from the groupconsisting of hydrofluoric, sulfuric, hydrochloric, nitric, phosphoric,hydrobromic, hydroiodic, acetic, chloroacetic, trichloroacetic, lactic,tartaric and polyacrylic.
 30. The composition according to claim 17wherein said oxidizing agent is hydrogen peroxide.
 31. The compositionaccording to claim 17 wherein said acid comprises hydrofluoric acid andthe coating-forming polymeric material is selected from epoxy orepoxy-acrylic material.
 32. The composition according to claim 31wherein said non-black solid pigment particles comprise a titaniumdioxide core, a first coating of an oxide comprising zirconia and asecond coating of an organic material.